1. Technical Field
The present invention relates to a piezoelectric driving device and a driving method therefor, and a robot and a driving method therefor.
2. Related Art
Piezoelectric actuators (piezoelectric driving devices) that drive driven members by vibrating piezoelectric bodies require no magnets or coils and are used in various fields (e.g. Patent Document 1 (JP-A-2004-320979)). In the basic configuration of the piezoelectric driving device, four piezoelectric elements are arranged in two rows and two columns on each of two surfaces of a reinforcing plate, and a total of eight piezoelectric elements are provided on both sides of the reinforcing plate. Each of the individual piezoelectric elements is a unit in which a piezoelectric body is sandwiched by two electrodes and the reinforcing plate is also used as one electrode of the piezoelectric element. A projecting portion for rotating a rotor as a driven member is provided in contact with the rotor on one end of the reinforcing plate. When an alternating-current voltage is applied to the diagonally provided two piezoelectric elements of the four piezoelectric elements, the two piezoelectric elements expand and contract and the projecting portion of the reinforcing plate performs reciprocating motion or elliptical motion in response thereto. Then, in response to the reciprocating motion or elliptical motion of the projecting portion of the reinforcing plate, the rotor as the driven member rotates in a predetermined rotation direction. Further, the two piezoelectric elements to which the alternating-current voltage is applied are switched to the other two piezoelectric elements, and thereby, the rotor may be rotated in the opposite direction. Patent Document 2 (JP-A-2008-227123) discloses a manufacturing method for a piezoelectric vibrator having a piezoelectric body. The piezoelectric body manufactured by the manufacturing method is the so-called bulk piezoelectric body and its thickness is 0.15 mm (150 μm).
In the case where a piezoelectric driving device is housed and used in a small space (e.g. within a joint of a robot), the wiring space may be insufficient with a piezoelectric driving device using a piezoelectric body of related art, and there has been a demand for a thinner piezoelectric body. However, if the piezoelectric body is made too much thinner, the force generated in the piezoelectric element becomes extremely small and displacement necessary for driving of the driven member is not obtained, and thus, it is necessary to increase the mechanical quality factor Qm for increasing the displacement. Further, it is necessary to suppress heat generation for housing of the piezoelectric driving device in the small space, and it is necessary to reduce mechanical loss with vibrations by increasing the mechanical quality factor Qm. As described above, in related art, an appropriate configuration of the small piezoelectric driving device that can drive the driven member is not sufficiently studied.